Improvements in waterproofing, compressive strength, durability, duration of packing during storage and other properties of Portland cement have been disclosed in U.S. Pat. Nos. 1,134,573; 1,772,999; 913,794; 1,076,028; and 1,305,645.
U.S. Pat. No. 1,134,573 relates to a method and means of producing an admixture by adding lime or bentonite to asphaltum oil or asphalt and mixing it with ordinary cement, water and aggregates to produce concrete or mortar. However, with the resulting concrete or mortar there may be partial leakage and the compressive strength, workability and duration of storage may not be preserved because the hydrophobic admixture has to be mixed with the unimproved traditional cement.
U.S. Pat. No. 1,772,999 relates to a process of producing an admixture by mixing diatomaceous earth or bentonite with mineral oil or animal oil, and coating Portland cement therewith. Further, this reference relates to a method for the production of an emulsion by mixing calcium chloride aqueous solution, which is used as a setting accelerator for concrete, with asphalt-dissolved crude oil mixed with bentonite or Fuller's earth. However, the quality of the resulting composition is not uniform because the admixture is made of natural oil and mineral material which are impure and weak in hardness as to decrease the strength and workability thereof. In addition, there may be more cracks in the concrete with an increase in the heat of hydration. Moreover, the reinforcing bars in the concrete can become corroded by the corrosive property of the calcium chloride.
U.S. Pat. No. 913,794relates to a method for producing a waterproof cement by coating the cement particles with a mixture obtained by admixing lime with an oleaginous substance without heating. However, the workability and waterproofing strength in the resulting concrete may be decreased because no pore filler is used for the cement other than wax and an oleaginous substance with lime.
U.S. Pat. No. 1,076,028 relates to a method for coating cement particles by passing the dry cement powder through a spray zone of a molten state of fatty acid soap or wax. However, the strength, waterproofing and workability of the resulting concrete is decreased because the cement is coated while it is forced through the spray zone.
U.S. Pat. No. 1,305,645 relates to a method for mixing cement with pitch powder pulverized below 100 mesh. However, there is a decrease in workability, strength and waterproofing in the resulting concrete because pitch has to be admixed with the cement during concreting.
The disadvantages of using ordinary Portland cement in producing concrete or mortar are discussed below.
In the conventional mixing of concrete or mortar with ordinary Portland cement, there must be a surplus of water, compared with the necessary amount of water used for hydration of cement, in order to enhance workability. Further, since air entraining necessarily occurs in concrete mixing, the surplus of water combined with the air entraining produces a lot of pore during hydration and setting. When the pores are interconnected, undesired leakage can occur.
In addition, the concrete or mortar formed with ordinary Portland cement has the problem of cracking due to the shrinkage and expansion caused by the heat of hydration and variations of the surrounding temperatures during and after hardening. These cracks are undesirable because they result in leakage.
Moreover, the conventional reinforced concrete using ordinary Portland cement has a drawback in that it creates a water pool beneath the aggregates or the horizontal reinforcing bars due to bleeding. This produces more pores and cracking under the heat of hydration.
Also, in the mixing of concrete or mortar with ordinary Portland cement, it is very difficult to keep a low water-content ratio, due to poor workability, unless air entraining admixtures are used.
Further, the concrete produced using ordinary Portland cement does not have satisfactory compressive strength after long periods of time.
In addition, ordinary Portland cement is highly water absorbent. This causes storage problems and results in hardening.
Moreover, additional waterproofing processes are required for concrete structures made with ordinary Portland cement. Not only is this very costly but also such processes cannot be used in a pressured area.
The durability of a reinforced concrete structure is closely related to the neutralization of the concrete material and corrosion of the reinforcing bars. After setting, if the alkalinity of the concrete is lost by the action of surface air or water, which contains carbon dioxide and sulfur dioxide, the concrete is neutralized. This causes corrosion of the reinforcing bars and destruction of the concrete.